Pulsed Laser Ablation Of A Specific Atmosphere In Thin Films

The interacting between laser beam and materials has been the focus of bothfundamental research and technology applications in related fields during the pastforty years since T.H. Maiman produced the first ruby laser in 1960. Scientificresearch and technological applications based on pulsed laser ablation (PLA) has beendeveloped. In this thesis, processes of PLA and characteristics of the plasma producedin vacuum and different background ambient were investigated. Methods anddynamics of pulsed laser deposition (PLD) assisted with active gas resources based onPLA in specific ambient gas were also examined and utilized on synthesis of severalkinds of thin films. By observing the temporal and spatial resolved optical emission spectra fromcopper plasma induced by laser ablation of a solid copper target, the dynamics of thegeneration of the plasma and the temporal revolution and spatial distribution of theplasma and the species within were examined. The results indicated that the plasmawas ignited by laser ablation of the copper target, and then the internal interactionsevolved from the optical breakdown and collision breakdown by hot electrons of thecopper vapor to the collisions between copper species and low-energy electrons. Atthe initial stage, the plasma was composed of large amounts of copper ions and highlyexcited copper atoms near the target surface, and then gradually dominated bylow-energy copper atoms and expanded away from the target. In addition to theslowdown and the confinement of the plasma expansion by the background gas, theionization and excitation of the ablated copper species were also facilitated bycollision with ambient gas molecules so that the optical emission lifetime wasprolonged. It is also found that the influence of the background gas on the ablatedspecies varies depending on their energy states. Methods of PLD combined with electron cyclotron resonance (ECR) plasma oratomic beam from a dc-plasma source were developed and utilized in deposition ofIII-nitrides films and B-C-N compound system films. Some compound films, such asAlN,GaN,BC,BCN and CNx were synthesized at low temperature. Aluminum nitride films have been prepared through two methods: basic pulsedlaser deposition from sintered aluminum nitride ceramics and ECR plasma-aidedreactive pulsed laser deposition from elemental aluminum metal. The band gap of thefilms obtained from basic PLD was found to be 5.6 eV, while that of the ECR-PLDprepared films to be 5.7 eV. Both of the AlN thin films luminesced from 325nm to复旦大学博士学位论文 3特定气氛中的脉冲激光烧蚀及其在薄膜制备上的应用550nm in PL test. GaN thin film from polycrystalline GaAs has been prepared byECR-PLD at low temperature. The band gap of the GaN film was determined to be3.4 eV and it luminesced from 350nm to 550nm in PL test. It was convinced that theexcitation of nitrogen by ECR microwave discharge could provide highly active gasambient for nitride films preparation and ECR-PLD provided a new method toproduce Group III nitrides films. BC and BCN films have been produced from a sintered B4C target by PLD andECR-PLD respectively. The average atomic ratio of B:C was 3:1 with 10% of oxygenimpurity in the BC film. Heating the substrate was beneficial to the structure of theBC film. The average atomic ratio of B:C:N was 3:1:3.8 with 46.1% nitrogen and5.6% oxygen in the BCN film, which mainly contained h-BN and other amorphousstructures. The BCN film had a high optical transmission from 1.4μm to 1.7μm. CNx films with rich nitrogen content have been prepared by pulsed laser ablationof graphite target combined with ECR discharge in nitrogen gas. Effects of differentDC biases applied to the substrate were studied while the film with nitrogen contentof 53% was achieved at a substrate bias of –50V. The results indicated that under anappropriate negative DC bias, bombardment of the growing...